This invention is concerned with structural modules which are in the form of rod elements pivotally joined by hub means so that the module may be collapsed into a compact bundle of rod elements and may be expanded into a frame. Devices of this general type are the subject of my prior U.S. Pat. Nos. 3,968,808; 4,026,313; 4,290,244; and 4,280,521. In all of these patents, the structures are "self supporting", i.e., they are characterized by the fact that structural integrity in the expanded form is achieved by stresses induced in the framework incidental to being expanded to full shape or form, without the aid of or necessity for an extraneous locking means. The Derus U.S. Pat. No. 4,276,726 also discloses a similar type of structure but further discloses an arrangement which achieves lock-up not by the aforesaid self-supporting action, but by means of a "releasable locking link" which is used to hold the structure in fully expanded form without imposing any self-induced stress in the rod elements. The module of this latter configuration involves a circumscribing series of pairs of crossed rod elements which are pivotally joined in scissored fashion. In collapsed form, these scissored pairs of rod elements form a bundle and in expanded form they describe, in zig-zag fashion, the side boundaries of a rectangular parallelepiped. The ends of the zig-zag related rod elements are joined by hub means, one group of which defines the corners of a square in one plane and the other group of which defines the corners of a second square in a second plane close to the first plane. Radiating inwardly from the corners defined by one group of hubs are a series of further rod elements whose inner ends are joined by a further hub. These latter rod elements and their related hubs limit the extent to which the structure may be expanded, this occuring when the aforesaid one group of hubs and the inwardly radiating rod elements are coplanar. The releasable locking means is operatively positioned when the structure has been expanded to prevent collapse of the structure by preventing the planes containing the two groups of hub means from moving apart.